How the flu turns deadly

This flu season is fierce and has already claimed the lives of at least 37 children in the United States, according to the Centers for Disease Control and Prevention.

There were 11,965 laboratory-confirmed flu-related hospitalizations reported from October 1 to January 20. The number of people infected with influenza is believed to be much higher because not everyone goes to their doctor when they are sick, nor do doctors test every patient.
Added to those scary stats, the World Health Organization estimates that annual flu epidemicsresult in about 3 to 5 million cases of severe illness globally and 290,000 to 650,000 deaths.
Although the fever and aches may feel terrible, most of us don't die from the flu. So how exactly does this common illness lead to so many dying?
"Influenza and its complications disproportionately affect people who are 65 and older. They account for 80% of the deaths," said Dr. William Schaffner, an infectious disease specialist at Vanderbilt University.
But young children and people who have an underlying illness, such as heart disease, lung disease or diabetes, are susceptible to dying from the flu as well, he said. There are three ways adults can succumb:

Pneumonia
"The usual flu death is a person who gets influenza, gets all that inflammation in their chest, and then has the complication of pneumonia," explained Schaffner, who added that this is a "long, drawn-out process."
Pneumonia is an infection that causes the small air sacs of the lungs to fill with fluid or pus. Though this is the most common route to death, flu can be fatal for more unusual reasons.

Sepsis
"Much of the systemic symptoms that any of us have with influenza -- the fever, the aches and pains, the sense of exhaustion -- all of those are part of (our body's) response to the virus," said Schaffner. The symptoms we experience are an inflammatory response to the immune system "soldiers" that our body sends to fight any pathogen, he said.
"Pushing the war analogy, we all know there is incidental damage that occurs during the course of a war," said Schaffner, and so the flu can also take a perfectly healthy person "and put them in the ER in 24 to 48 hours."
Flu stimulates an immune response in everyone's body, but for some people, this natural response can be "overwhelming," noted Schaffner. "Young robust people can have such an overwhelming response that it's called a cytokine storm." Cytokines -- proteins that are created as part of the inflammatory response -- create a "storm" in the body, explained Schaffner: "And this cytokine storm can actually lead to sepsis in the person."
Kyler Baughman, 21, is one example of that happening. He died unexpectedly in December at UPMC Presbyterian Hospital in Pittsburgh after a bout with the flu. Baughman, a college student, worked two jobs and often posted pictures of himself at the gym on social media. The cause of his death, as reported by the Allegheny County Medical Examiner, was influenza, septic shock and multiple organ failure.

Heart attack
Chances of a heart attack are increased sixfold during the first seven days after a flu infection, a new study published Wednesday in the New England Journal of Medicine found. The study looked at nearly 20,000 cases of flu in Ontario adults age 35 or older.
The risk may be higher for older adults, said Dr. Jeff Kwong, lead author of the study and a scientist at the Institute for Clinical Evaluative Sciences and Public Health Ontario. Heart attack occurs when blood flow to the heart is abruptly cut off; this is also called acute myocardial infarction.
Since a few days usually elapse between getting sick and getting a lab test, Kwong said "the increased risk is probably within the first 10 days or so after exposure to the virus."
The research, which identified 364 hospitalizations for acute myocardial infarction among the flu cases studied, also showed a stronger association for influenza B than influenza A. "We would have needed more cases to determine if the difference was real or just a chance finding," said Kwong.
Though the new study did not identify the reasons why flu might lead to heart attack, Kwong and his co-authors theorize that infectious illness may cause inflammation, stress and constriction of blood vessels, which increases blood pressure.
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How the flu turns deadly